Imaging lens

ABSTRACT

A compact imaging lens which addresses low-profile and low F value, and corrects aberrations. An imaging lens includes a first lens having positive refractive power and a convex surface on an object side near an optical axis, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens and a eighth lens having a concave surface on an image side near the optical axis as double-sided aspheric lens, wherein the second to seventh lenses each have at least one aspheric surface, and the eighth lens has pole points off an optical axis on the aspheric image-side surface.

The present application is based on and claims priority of Japanesepatent application No. 2015-248792 filed on Dec. 21, 2015, the entirecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an imaging lens which forms an image ofan object on a solid-state image sensor such as a CCD sensor or a C-MOSsensor used in a compact imaging device, and more particularly to animaging lens which is built in an imaging device mounted in anincreasingly compact and low-profile mobile phone, smartphone, or PDA(Personal Digital Assistant), or a game console, or an informationterminal such as a PC and a robot, or a home appliance or a car with acamera function.

Description of the Related Art

In recent years, it becomes common that a camera function is mounted inmany information terminals. Furthermore, it becomes reuuisites to mountthe camera in mobile terminals, such as the mobile phone, smartphone, orPDA (Personal Digital Assistant) as an additional value to the products.Not only the mobile terminals, there has been increased demand ofproducts to which a camera function is added, such as a wearable device,a game console, PC, a home appliance, and a drone, and development ofsuch products may be rapidly proceeded. Recently, a display device builtin the above information terminals becomes large and achieveshigh-definition, therefore high pixalation is required for an imaginglens. The imaging lens to be mounted is required to have furtherhigh-performance.

Demand of compactness in the imaging device is still strong. Therefore,regarding the image sensor, in order to realize compactness whilemaintaining high pixel, micronizing of pixel size has been rapidlyproceeded. If the pixel size of the image sensor becomes small, receivedluminous quantity per one pixel is decreased and deterioration in imagequality by noise becomes serious problem. In order to solve the problem,a bright optical system is required for the imaging lens, and demand ofa lens having a large diameter of F1.9 or less is increased.

However, realization of the imaging lens satisfying low-profileness andlow f-value at the same time difficult, especially aberration correctionin a peripheral area is difficult. Therefore, there is problem to secureproper optical performance throughout the image.

There is known a conventional imaging lens composed of eight constituentlenses, such as that disclosed in Patent Literature 1.

Patent Document 1 (JP-A-2001-13405) discloses an imaging lens havingeight constituent lenses, which is composed of, in order from an objectside, a first lens group having negative refractive power, a second lensgroup having positive refractive power and a third lens group havingpositive refractive power. The first lens group comprises, in order, apositive lens and a meniscus negative lens having a convex surface on anobject side, the second lens group comprises, in order, a positive lens,a negative lens and a positive lens, and the third lens group comprises,in order, a double-sided concave lens having a strong curvature on theobject side, a meniscus positive lens having a convex surface on animage side, and a positive lens. An aperture is provided between thesecond lens group and the third lens group.

The imaging lens disclosed in the above Patent Literature 1 is relatedto an exchange lens for a 35 mm single lens reflex camera, which hasonly eight constituent lenses without using aspheric surfaces, and largediameter and high-performance and is compact, and its purpose is tolargely reduce cost in production. This lens achieves brightness of F2.1The total length becomes 50 mm or more because it is used for a singlelens reflex camera, and it is very difficult to apply to the mobileterminals or information devices. If there are realized low-profilenessand further low F-value, by means of the lens constitution disclosed inPatent Literature 1, all of surfaces are spherical and it is difficultin aberration correction in a peripheral area and it can not be obtainedhigh optical performance required in recent years.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above problem, and anobject thereof is to provide an imaging lens which is compact andlow-profile applicable for the above mobile terminals and informationterminals, satisfies demand of low F-value in well balance, properlycorrect aberrations and has high resolution thereby.

Here, low-profile implies that total track length is 18 mm or less, andratio of the total track length and the diagonal length of the effectiveimaging plane of the image sensor (a ratio of total track length todiagonal length) is about 1.3. Low F-value implies brightness havingF1.8 or less. The diagonal length showing a ratio of total track lengthto diagonal length is twice length of the maximum image height, that is,the vertical height from an optical axis to the point where a light rayincident on the imaging lens at a maximum field of view enters andforming an image on the image plane, and considered as the sameparameter as diagonal length of an effective imaging plane of the imagesensor.

In the present invention, a convex surface or a concave surface meansthat the paraxial portion of the surface (portion near the optical axis)is convex or concave. A pole point is defined as an off-axial point onan aspheric surface at which a tangential plane intersects the opticalaxis perpendicularly. The total track length is defined as distance froman object-side surface to an image-side surface of an optical elementlocated nearest to the object side, when the thickness of an opticalelement not involved in divergence or convergence of light, such as anIR cut filter or cover glass, is air-converted.

An imaging lens according to the present invention which forms an imageof an object a solid-state image sensor, in which the lenses arearranged in order from an object side to an image side, comprising:

a first lens having positive refractive power and a convex surface on anobject side near an optical axis, a second lens, a third lens, a fourthlens, a fifth lens, a sixth lens, a seventh lens and a eighth lenshaving a concave surface on an image side near the optical axis asdouble-sided aspheric lens, wherein said second to seventh lenses eachhave at least one aspheric surface, and the eighth lens has pole pointsoff an optical axis on the aspheric image-side surface.

In the imaging lens having the above structure, low-profileness isachieved by strengthening positive refractive power of the first lens.Because the second to seventh lenses has each have at least one asphericsurface, correction of spherical aberrations, astigmatism, fieldcurvature and distortion is made in well balance while maintaininglow-profileness. The eighth lens has a concave surface on the image sidenear the optical axis and aspherical surface on both sides, and correctsspherical aberrations, field curvature in a peripheral area anddistortion by means of an aspheric surface formed on both surfaces. Theimage-side surface of the eighth lens has pole points and aspheric shapeand light ray incident angle of ray incident on the image sensor is madeappropriate.

The imaging lens having the above structure preferably satisfies a belowconditional expression (1);

0.5<Σd/f<2.1   (1)

where f denotes the focal length of the overall optical system, and Σddenotes a distance on an optical axis from the object-side surface of afirst lens to the image-side surface of the eighth lens.

The conditional expression (1) defines a distance on the optical axisfrom the object-side surface of the first lens to the image-side surfaceof the eighth lens to the focal length of the overall optical system,and it is a condition for shortening a total track length. When thevalue is above the upper limit of the conditional expression (1), lengthin the optical axis becomes too long, and shortening the total tracklength becomes difficult. On the other hand, if the value is below thelower limit of the conditional expression (1), the focal length of theoverall optical system becomes too long relatively and field of viewbecomes narrow. Thereby, each lens can not secure enough thickness or anedge thickness.

All of the imaging lenses having the above structure are preferablyarranged with an air interval to a lens adjacent each other.

All of the imaging lenses are arranged with an air interval withoutjoining lens surface of lenses adjacent each other, and the number ofsurface on which an aspheric surface is formed is increased, appropriatecorrection of aberrations can be made thereby.

The imaging lens having the above structure preferably satisfies thebelow conditional expression (2).

0.1<Ph82/ih<0.9   (2)

where Ph82 denotes a height perpendicular to the optical axis of thepole point formed on an image-side surface of the eighth lens; ihdenotes maximum image height.

The conditional expression (2) defines a height perpendicular to theoptical axis of the pole point formed on the image-side surface of theeighth lens regarding an image size. If the conditional expression (2)is satisfied, it becomes possible to properly correct off-axialastigmatism and deterioration in field curvature due to low-profilenessand low F-value of the imaging lens.

According to the imaging lens having the above structure, the secondlens preferably has a concave surface on the object side near theoptical axis.

If the second lens has a concave surface on the object side, arefractive angle of an incident ray becomes small and it becomes easy tosuppress higher-order aberration generated on this surface.

According to the imaging lens having the above structure, the third lensis preferable to be meniscus near the optical axis

If the third lens becomes meniscus near the optical axis, the fieldcurvature can be properly corrected.

According to the imaging lens having the above structure, if the firstto sixth lenses are grouped as a front group, composite refractive powerof the front group is preferably positive, and if the seventh and eighthare grouped as a rear group, composite refractive power of the reargroup is preferably negative. By allocating such refractive power, photoproperties can be maintained.

According to the imaging lens having the above structure, the seventhand eighth lenses preferably have negative refractive power.

The seventh and eighth lenses have negative refractive power and itbecomes possible to share negative refractive power in two lensesarranged on the image side in well balance. Accordingly, an angle of theincident ray is controlled and astigmatism is corrected, and it becomeseffective for control of an incident angle of a main light lay to theimage sensor, and appropriate correction of field curvature anddistortion.

According to the imaging lens having the above structure, the seventhlens is preferable to be meniscus near the optical axis.

The seventh lens is formed as meniscus near the optical axis andpreferable correction on field curvature can be possible.

The imaging lens having the above structure preferably satisfies thebelow conditional expression (3).

0.3<|r13/r14|<4.9   (3)

where r13 denotes the curvature radius near an optical axis of theobject-side surface of the seventh lens, and r14 denotes the curvatureradius near the optical axis of the image-side surface of the seventhlens.

The conditional expression (3) defines relation of the Curvature radiusnear the optical axis of the object side and the image side of theseventh lens, and it is a condition to properly correct sphericalaberration and to moderate sensibility to shortening of the total tracklength and production error. If the seventh lens is meniscus and has aconvex surface on the object side near the optical axis, when a value isabove the upper limit of the conditional expression (3), refractivepower on the image-side surface of the seventh lens becomes too strong.Thereby, aberrations generated on this surface are increased and thesensitivity to the product error is increased. On the other hand, if theseventh lens is meniscus and has a concave surface on the object sidenear the optical axis, when a value is below the lower limit of theconditional expression (3), refractive power of the object-side surfaceof the seventh lens becomes too strong. Thereby, aberrations generatedon this surface are increased and the sensitivity to the product erroris increased.

According to an imaging lens having the above structure, the eighth lenspreferably adopts plastic material.

The eighth lens adopts the plastic material and aspheric shape providedon both surfaces can be stably obtained and cost may be reduced.

According to an imaging lens having the above structure, the conditionalexpression (4) below is preferably satisfied,

0.2<r16/f<0.8   (4)

where r16 denotes the curvature radius of the image-side surface of theeighth lens, and f denotes a focal length of the overall optical system.

The conditional expression (4) defines a condition for properly settingthe curvature radius on the image-side surface of the eighth lens, andalso the condition for suppressing generation of astigmatism, comaaberration and distortion and low-profileness. When a value is above theupper limit of the conditional expression (4), negative refractive poweron the image-side surface of the eighth lens becomes too weak, and itbecomes difficult to correct astigmatism and coma aberration. On theother hand, when the value is below the lower limit of the conditionalexpression (4), negative refractive power on the image-side surface ofthe eighth lens becomes too strong, and it becomes difficult to shortenthe total track length and correct distortion.

The imaging lens having the above structure preferably satisfies thebelow conditional expression (5),

0.4<|f/f7|+|f/f8|<2.2   (5)

where f denotes a focal length of the overall optical system, f7 denotesa focal length of the seventh lens, and f8 denotes a focal length of theeighth lens.

The conditional expression (5) properly defines appropriate range offocal lengths of the seventh and eighth lenses, respectively, and whenthe conditional expression is satisfied, the total track length can beeffectively shortened.

The imaging lens having the above structure preferably satisfies thebelow conditional expression (6),

15<νd8−νd7<52   (6)

where νd7 denotes an Abbe number of the seventh lens at d-ray, and νd8is an Abbe number of the eighth lens at d-ray.

The conditional expression (6) properly defines appropriate range ofAbbe number of the seventh and eighth lenses at d-ray and is a conditionfor proper correction of chromatic aberrations. Materials satisfying theconditional expression (6) are adopted, and chromatic aberrations can beproperly corrected. The material within a range of the conditionalexpression shows availability of selecting low-cost plastics andcontributes to reduce cost.

The imaging lens having the above structure preferably satisfies thebelow conditional expression (7),

f123/f<3.5   (7)

where f denotes a focal length of the overall optical system, f123denotes a composite focal length of the first, second and third lenses.

The conditional expression (7) defines relation of the composite focallength of the first, second and third lenses and a focal length of theoverall optical system. When a value is above the upper limit of theconditional expression (7), the composite focal length of the first,second and third lenses becomes too weak and it becomes difficult toshorten the total track length.

The imaging lens having the above structure preferably satisfies thebelow conditional expression (8),

−1.9<f/f8<−0.07   (8)

where f denotes a focal length of the overall optical system, f8 denotesa focal length of the eighth lens.

The conditional expression (8) defines relation a focal length of theoverall optical system of the imaging lens and a focal length of theeighth lens. When a value is above the upper limit of the conditionalexpression (8), negative refractive power of the eighth lens become tooweak, and it becomes difficult to correct field curvature. On the otherhand, when the value is below the lower limit of the conditionalexpression (8), negative refractive power of the eighth lens becomes toostrong, and it is not preferable that an incident angle of a main lightlay to the image plane (an image sensor) becomes too large.

The imaging lens having the above structure preferably satisfies thebelow conditional expression (9),

0.6<TTL/2ih<1.3   (9)

where TTL denotes a total track length, ih denotes maximum image height.

The conditional expression (9) defines ratio of total track length todiagonal length. When a value is above the upper limit of theconditional expression (9), the total track length becomes too long andit becomes difficult to respond demand of low-profileness. On the otherhand, when the value is below the lower limit of the conditionalexpression (9), the total track length becomes too short therefore, itis not preferable that the correction of aberrations becomes difficultand error sensitivity at production becomes increased.

The imaging lens having the above structure preferably satisfies thebelow conditional expression (10),

0.5<ih/f<0.9   (10)

where f denotes a focal length of the overall optical system, ih denotesmaximum image height.

The conditional expression (10) defines appropriate range ofphotographing field of view. When a value is above the upper limit ofthe conditional expression (10), the field of view becomes too large toproperly correct aberrations. Therefore, it becomes difficult to correctaberrations in peripheral area of the image, and deterioration in imagequality may occur easily. On the other hand, when the value is below thelower limit of the conditional expression (10), correction ofaberrations can be easily performed, however, addressing wide field ofview is not enough.

The imaging lens having the above structure preferably satisfies thebelow conditional expression (11),

Fno≦1.8   (11)

where Fno denotes F-number.

The conditional expression (11) defines F-number. If a pixel size of theimage sensor becomes small, luminous quantity took from the imaging lenshas tendency to be reduced and it becomes difficult to obtain brightimage. If this problem is to be solved by increasing sensitivity at theimage sensor side, there is generated noise and deterioration in imageeasily occurred. Therefore, it is an effective means to increaseluminous quantity emitted from the imaging lens. If the conditionalexpression (11) is satisfied, addressing an image sensor recentlydensifed can be available.

The imaging lens having the above structure preferably satisfies thebelow conditional expression (12),

|f/f4|+|f/f5|+|f/f6|<2.8   (12)

where f denotes a focal length of the overall optical system, f4 denotesa focal length of the fourth lens, f5 denotes a focal length of thefifth lens, f6 denotes a focal length of the sixth lens.

Conditional expression (12) defines appropriate range of a focal lengthof the fourth lens, fifth lens and sixth lens, respectively. When avalue is above the upper limit, power of optical system of the fourth tosixth lenses becomes too large and it is not preferable that thesensitivity to the production error becomes sensitive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the general configuration of animaging lens in Example 1 according to an embodiment of the presentinvention;

FIG. 2 shows spherical aberration, astigmatism, and distortion of theimaging lens in Example 1 according to the embodiment of the presentinvention;

FIG. 3 is a schematic view showing the general configuration of animaging lens in Example 2 according to the embodiment of the presentinvention;

FIG. 4 shows spherical aberration, astigmatism, and distortion of theimaging lens in Example 2 according to the embodiment of the presentinvention;

FIG. 5 is a schematic view showing the general configuration of animaging lens in Example 3 according to the embodiment of the presentinvention;

FIG. 6 shows spherical aberration, astigmatism, and distortion of theimaging lens in Example 3 according to the embodiment of the presentinvention;

FIG. 7 is a schematic view showing the general configuration of animaging lens in Example 4 according to the embodiment of the presentinvention;

FIG. 8 shows spherical aberration, astigmatism, and distortion of theimaging lens in Example 4 according to the embodiment of the presentinvention;

FIG. 9 is a schematic view showing the general configuration of animaging lens in Example 5 according to the embodiment of the presentinvention;

FIG. 10 shows spherical aberration, astigmatism, and distortion of theimaging lens in Example 5 according to the embodiment of the presentinvention;

FIG. 11 is a schematic view showing the general configuration of animaging lens in Example 6 according to the embodiment of the presentinvention;

FIG. 12 shows spherical aberration, astigmatism, and distortion of theimaging lens in Example 6 according to the embodiment of the presentinvention;

FIG. 13 is a schematic view showing the general configuration of animaging lens in Example 7 according to the embodiment of the presentinvention;

FIG. 14 shows spherical aberration, astigmatism, and distortion of theimaging lens in Example 7 according to the embodiment of the presentinvention;

FIG. 15 shows a view showing height Ph82 perpendicular to the opticalaxis of the pole point formed on an image-side surface of the eighthlens according to the eighth lens of the image sensor related to thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, the preferred embodiment of the present invention will bedescribed in detail referring to the accompanying drawings. FIGS. 1, 3,5, 7, 9, 11 and 13 are schematic views showing the generalconfigurations of the imaging lenses in Examples 1 to 7 according tothis embodiment, respectively. Embodiment of the present invention isexplained below.

As shown in each drawing, the imaging lens according to this embodimentcomprises, in order from an object side to an image side, a first lensL1 having positive refractive power and a convex surface on an objectside near an optical axis, a second lens L2 having at least one asphericsurface, a third lens L3 having at least one aspheric surface, a fourthlens L4 having at least one aspheric surface, a fifth lens L5 having atleast one aspheric surface, a sixth lens L6 having at least one asphericsurface, a seventh lens L7 having at least one aspheric surface, and aneighth lens L8 having a concave surface on an image side near theoptical axis as double-sided aspheric lens, wherein the eighth lens L8has pole points Ph82 off an optical axis on the aspheric image-sidesurface.

In each embodiment, variety of selection is available such thatrefractive power of the second lens L2 to the eighth lens L8 is positiveor negative, shape of the image-side surfaces of the first lens L1 tothe seventh lens L7, respectively is a convex or concave near an opticalaxis, and an optimum selection is made so as to realize performance atan early stage.

More specifically, power arrangement in the embodiment 1 is, in orderfrom an object side, +−+−+−−−, in the embodiments 2 and 3, the powerarrangement is, in order from the object side, +−+−++−−, in theembodiments 4 to 6, the power arrangement is, in order from the objectside, ++−+−+−−, and in the embodiment 7, the power arrangement is, inorder from the object side, ++−+++−−. The following condition is commonto all of embodiment, namely the first lens L1 has positive refractivepower, and the seventh lens L7 and the eighth lens L8 have negativerefractive power. Shape of each lens surface is defined through theembodiment 1 to 7 that the object-side surface of the first lens L1 andthe second lens L2 are convex near the optical axis, the image-sidesurface of the eighth lens L8 is concave near the optical axis, thethird lens L3 and the seventh lens L7 are meniscus near the opticalaxis.

An aperture stop ST is located between the first lens L1 and the secondlens L2. The location of the aperture stop ST may be, as shown in FIG.5, between the second lens L2 and the third lens L3.

A filter IR such as an IR cut filter or a cover glass is located betweenthe eighth lens L8 and an image plane IMG. The filter IR is omissible. Apoint forming an image on the image plane in an optical system isvariable due to thickness of the filter IR, and a distance of adirection of the optical axis according to the present invention isdefined as a distance which the thickness of an optical element notinvolved in divergence or convergence of light is air-converted.

Next, description of the present embodiments will be made with referenceto FIG. 1.

According to the present embodiment, the first lens L1 is biconvex nearthe optical axis, and low-profileness can be achieved by adding strongpositive refractive power. Shape of the first lens L1 is not limited tobiconvex, but may be meniscus and convex surface on the object side nearthe optical axis as shown in the embodiment 6 in FIG. 11.

The second lens L2 is meniscus and has concave surface on the image sidenear the optical axis, and also has negative refractive power asdouble-sided aspheric lens. Shape or refractive power of the second lensL2 is not limited to the above. The embodiments 4, 5 and 7 shown inFIGS. 7, 9, and 13, respectively are examples having positive refractivepower and biconvex surfaces near the optical axis. The embodiment 6shown in FIG. 11 is an example of meniscus having positive refractivepower and convex surface on the object side near the optical axis.

The third lens L3 is meniscus and has positive refractive power andconvex surface on the object side near the optical axis as double-sidedaspheric lens. Shape or refractive power of the third lens L3 is notlimited to the above. As shown in the embodiments 2 and 3 in FIGS. 3 and5, the third lens L3 may be meniscus and have a convex surface on theimage side near the optical axis. The embodiments 4, 5, 6 and 7 shown inFIGS. 7, 9, 11 and 13, respectively are an example that the refractivepower of the third lens L3 becomes negative.

The fourth lens L4 is meniscus and has negative refractive power and aconcave surface on the image side near the optical axis as double-sidedaspheric lens. Shape or refractive power of the fourth lens L4 is notlimited to the above. The embodiment 4 shown in FIG. 7 is an examplethat the fourth lens is meniscus and has positive refractive power and aconcave surface on the object side near the optical axis, and theembodiments 5, 6, and 7 shown in FIGS. 9, 11 and 13 is an example tohave positive refractive power and a biconvex surfaces on the object andimage sides near the optical axis.

The fifth lens L5 is meniscus and has positive refractive power and aconcave surface on the object side near the optical axis as double-sidedaspheric lens. Shape or refractive power of the fifth lens L5 is notlimited to the above. As the embodiment 2 shown in FIG. 3, the fifthlens L5 may have positive refractive power and biconvex surfaces on theobject and image sides near the optical axis, or as the embodiments 3and 7 shown in FIGS. 5 and 13, may be meniscus and have positiverefractive power and concave surface on the image side near the opticalaxis. Further, as the embodiments 4, 5 and 6 shown in FIGS. 7, 9 and 11,the fifth lens L5 may be meniscus and have negative refractive power anda concave surface on the image side near the optical axis.

The sixth lens L6 is meniscus and has negative refractive power and aconcave surface on the image side near the optical axis as double-sidedaspheric lens. Shape or refractive power of the sixth lens L6 is notlimited to the above. The embodiments 2, 3, 4, 5 and 6 shown in FIGS. 3,5, 7, 9 and 11 are examples being meniscus and having positiverefractive power and a concave surface on the object side near theoptical axis, and the embodiment 7 shown in FIG. 13 is an example havingpositive refractive power and biconvex surfaces on the object and imagesides near the optical axis.

As mentioned, appropriate positive or negative refractive powers areprovided to the second lens L2 to the sixth lens L6 and each surface isformed as aspherical, therefore various aberrations such as sphericalaberrations, astigmatism, field curvature and distortion are correctedwhile maintaining low-profileness.

The seventh lens L7 is meniscus and has negative refractive power and aconcave surface on the image side near the optical axis as double-sidedaspheric lens. Shape of the seventh lens L7 is not limited to themeniscus having a concave surface on the image side near the opticalaxis. As the embodiments 2 and 3 shown in FIGS. 3 and 5, it may bemeniscus and have a concave surface on the object side near the opticalaxis.

The eighth lens L8 is meniscus and has negative refractive power and aconcave surface on the image side near the optical axis as double-sidedaspheric lens. The aspheric surfaces formed on both side correctspherical aberrations, field curvature in a peripheral area, anddistortion. The image-side surface of the eighth lens L8 has theaspherical shape having the pole points Ph82 off an optical axis, and anappropriate light ray incident angle on the image sensor IMG isprovided. Shape of the eighth lens L8 is not limited to the meniscushaving a concave surface on the image side near the optical axis. Theembodiment 4 shown in FIG. 7 is an example to have biconcave surfaces onthe object and image sides near the optical axis.

According to the imaging lens having the above structure, if the firstlens L1 to sixth lens L6 are grouped as a front group, compositerefractive power of the front group is positive, and if the seventh lensL7 and eighth lens L8 are grouped as a rear group, composite refractivepower of the rear group is negative. Using such refractive powerdistribution, telephoto properties can be maintained.

The imaging lens according to the present embodiments adopts plasticmaterials to all of lenses, therefore manufacturing becomes easy andmass-production is available at low cost. Furthermore, asphericalsurfaces are formed can both sides of all lenses and aberrations areproperly corrected.

Note that the material adopted to the lens is not limited to the plasticmaterial. If glass material having a large power is used for the lenses,it becomes possible to suppress deterioration in the image caused bymovement of an image accompanying change of an atmospheric temperatureand further high-performance may be aimed. All of surfaces of lenses arepreferably formed as aspherical, however, spherical surfaces may beadopted which is easy to manufacture in accordance with requiredperformance.

The imaging lens according to the present embodiments shows preferableeffect by satisfying the below conditional expressions (1) to (12).

0.5<Σd/f<2.1   (1)

0.1<Ph82/ih<0.9   (2)

0.3<|r13/r14|<4.9   (3)

0.2<r16/f<0.8   (4)

0.4<|f/f7|+|f/f8|<2.2   (5)

15<νd8−νd7<52   (6)

f123/f<3.5   (7)

−1.9<f/f8<−0.07   (8)

0.6<TTL/2ih<1.3   (9)

0.5<ih/f<0.9   (10)

Fno≦1.8   (11)

|f/f4|+|f/f5|+|f/f6|<2.8   (12)

where

Σd: a distance on an optical axis X from the object-side surface of afirst lens to the image-side surface of the eighth lens

Ph82: a height perpendicular to the optical axis X of the pole pointformed on an image-side surface of the eighth lens

ih: maximum image height

f: a focal length of the overall optical system

f4: a focal length of the fourth lens L4

f5: a focal length of the fifth lens L5

f6: a focal length of the sixth lens L6

f7: a focal length of the seventh lens L7

f8: a focal length of the eighth lens L8

f123: a composite focal length of the first, second and third lenses

r13: curvature radius near an optical axis of the object-side surface ofthe seventh lens L7

r14: curvature radius near an optical axis of the image-side surface ofthe seventh lens L7

r16: curvature radius near an optical axis of the image-side surface ofthe eighth lens L8

Fno: F-number

νd7: abbe number at d-ray of the seventh lens L7

νd8: abbe number at d-ray of the eighth lens L8

TTL: total track length.

Furthermore, the imaging lens according to the present embodiments showspreferable effect by satisfying the below conditional expressions (1a)to (12a).

0.77<Σd/f<1.74   (1a)

0.24<Ph82/ih<0.72   (2a)

0.45<|r13/r14|<4.08   (3a)

0.28<r16/f<0.65   (4a)

0.6<|f/f7|+|f/f8|<1.81   (5a)

23<νd8−νd7<43   (6a)

f123/f<2.91   (7a)

−1.59<f/f8<−0.1   (8a)

0.77<TTL/2ih<1.19   (9a)

0.57<ih/f<0.81   (10a)

1.0≦Fno≦1.8   (11a)

|f/f4|+|f/f5|+|f/f6|<2.32   (12a)

The signs in the above conditional expressions have the same meanings asthose in the paragraph before the preceding paragraph.

Additionally, the imaging lens according to the present embodimentsshows more preferable effect by satisfying the below conditionalexpressions (1b) to (10b), and (12b).

0.91≦Σd/f≦1.56   (1b)

0.31≦Ph82/ih≦0.63   (2b)

0.52≦r13/r14<≦3.67   (3b)

0.32≦r16/≦f0.57   (4b)

0.7≦f/f7|+|f/f8|1.62   (5b)

26<νd8−νd7<39   (6b)

f123/f≦2.61   (7b)

−1.43≦f/f8≦−0.12   (8b)

0.86≦TTL/2ih≦1.14   (9b)

0.60≦ih/f≦0.77   (10b)

|f/f4|+|f/f5|+|f/f6|≦2.08   (12b)

The signs in the above conditional expressions have the same meanings asthose in the paragraph before the preceding paragraph.

FIG. 15 shows points of parameter Ph82 in the conditional expressions(2), (2a) and (2b). As shown in FIG. 15, the pole point Ph82 formed onthe image-side surface of the eighth lens L8 is defined as an off-axialpoint on an aspheric surface at which a tangential plane intersects theoptical axis X perpendicularly.

The aspheric shapes of these lens surfaces are expressed by Equation 1,where Z denotes an axis in the optical axis direction, H denotes aheight perpendicular to the optical axis, k denotes a conic constant,and A4, A6, A8, A10, A12, A14, and A16 denote aspheric surfacecoefficients.

$\begin{matrix}{Z = {\frac{\frac{H^{2}}{R}}{1 + \sqrt{1 - {( {k + 1} )\frac{H^{2}}{R^{2}}}}} + {A_{4}H^{4}} + {A_{6}H^{6}} + {A_{8}H^{8}} + {A_{10}H^{10}} + {A_{12}H^{12}} + {A_{14}H^{14}} + {A_{16}H^{16}}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

Next, examples of the imaging lens according to this embodiment will beexplained. In each example, f denotes the focal length of the overalloptical system of the imaging lens, Fno denotes an F-number, ω denotes ahalf field of view. Additionally, i denotes surface number counted fromthe object side, r denotes a curvature radius, d denotes the distance oflenses on the optical axis (surface distance), Nd denotes a refractiveindex at d-ray (reference wavelength), and νd denotes an Abbe number atd-ray. As for aspheric surfaces, an asterisk (*) is added after surfacenumber i.

EXAMPLE 1

TABLE 1 Table 1 Unit [mm] f = 11.68 Fno = 1.4 ω(°) = 33.7 Surface DataSurface Curvature Surface Refractive Abbe Number i Radius r Distance dIndex Nd Number νd (Object) Infinity Infinity  1* 9.753 1.900 1.544355.86 (=νd1)  2* −44.764 0.097  3(Stop) Infinity 0.030  4* 6.390 0.6971.6503 21.54 (=νd2)  5* 4.407 1.119  6* 14.111 1.343 1.5348 55.66 (=νd3) 7* 66.576 1.559  8* 73.582 1.714 1.5348 55.66 (=νd4)  9* 67.528 0.64510* −21.307 1.393 1.5443 55.86 (=νd5) 11* −5.897 0.022 12* 12.113 1.8731.6503 21.54 (=νd6) 13* 8.925 0.935 14* 10.383 (=r13)  0.725 1.650321.54 (=νd7) 15* 5.263 (=r14) 0.381 16* 5.002 0.918 1.5348 55.66 (=νd8)17* 4.227 (=r16) 0.660 18 Infinity 0.800 1.5168 64.20 19 Infinity 0.503Image Plane Infinity Constituent Lens Data Lens Start Surface FocalLength 1 1 14.90 2 4 −25.35 3 6 33.19 4 8 −1702.49 5 10 14.52 6 12−67.86 7 14 −17.38 8 16 −86.89 Composite Focal Length Lens Focal Length1, 2, 3 16.74 Aspheric Surface data First Second Fourth Fifth SixthSeventh Eighth Ninth Surface Surface Surface Surface Surface SurfaceSurface Surface k 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 A4 5.072E−04 3.442E−04 −6.434E−03 −8.339E−03  −1.196E−03  −2.194E−03 −2.873E−03  −2.525E−03  A6−4.305E−05  1.779E−05 4.044E−04 4.662E−04 −3.742E−05  −7.404E−07−1.631E−05  −1.271E−05  A8 2.860E−06 −1.518E−06  −2.178E−05  −2.978E−05 3.490E−06 −6.546E−07 2.138E−06 −2.625E−07  A10 −6.362E−08  2.437E−084.977E−07 8.280E−07 −4.032E−07  −1.138E−07 0.000E+00 0.000E+00 A120.000E+00 0.000E+00 0.000E+00 −1.185E−08  0.000E+00  0.000E+00 0.000E+000.000E+00 A14 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 A16 0.000E+00 0.000E+00 0.000E+000.000E+00 0.000E+00  0.000E+00 0.000E+00 0.000E+00 Tenth EleventhTwelfth Thirteenth Fourteenth Fifteenth Sixteenth Seventeenth SurfaceSurface Surface Surface Surface Surface Surface Surface k 0.000E+00−4.857E−01  0.000E+00 0.000E+00 0.000E+00 −6.680E+00 −1.215E+01 −7.779E+00  A4 −3.847E−04  9.510E−05 −1.359E−03  −3.401E−04  −4.966E−03 −3.832E−03 −4.134E−03  −2.513E−03  A6 8.615E−05 1.348E−04 2.994E−05−1.744E−04  6.239E−05  1.186E−04 1.323E−04 9.012E−05 A8 −8.016E−06 −8.071E−06  −1.198E−05  1.033E−05 4.058E−06 −2.411E−06 −2.545E−06 −2.544E−06  A10 1.611E−07 1.792E−07 8.770E−07 −3.467E−07  −1.593E−07  4.486E−08 4.418E−08 4.820E−08 A12 0.000E+00 0.000E+00 −2.910E−08 7.165E−09 2.270E−09 −4.991E−10 −4.917E−10  −4.812E−10  A14 0.000E+000.000E+00 3.573E−10 −8.677E−11  −1.419E−11   1.810E−12 2.044E−121.817E−12 A16 0.000E+00 0.000E+00 0.000E+00 4.750E−13 2.797E−14 0.000E+00 0.000E+00 0.000E+00

Basic lens data are shown in below Table 1.

The imaging lens in Example 1 satisfies all of conditional expressions(1) to (12) as shown in Table 8.

FIG. 2 shows spherical aberration (mm), astigmatism (mm), and distortion(%) of the imaging lens in Example 1. The spherical aberration diagramshows the amount of aberration at wavelengths of F-ray (486 nm), d-ray(588 nm), and C-ray (656 nm). The astigmatism diagram and distortiondiagram show the amount of aberration at d-ray. The astigmatism diagramshows sagittal image surface S and the amount of aberration t d-ray ontangential image surface T (same as in FIGS. 4, 6, 8, 10, 12, and 14).As shown in FIG. 2, each aberration is corrected properly.

EXAMPLE 2

Basic lens data are shown in below Table 2.

TABLE 2 Table 2 Unit [mm] f = 7.75 Fno = 1.6 ω(°) = 33.0 Surface DataSurface Curvature Surface Refractive Abbe Number i Radius r Distance dIndex Nd Number νd (Object) Infinity Infinity  1* 4.183 1.150 1.544355.86 (=νd1)  2* −25.354 0.000  3(Stop) Infinity 0.030  4* 3.355 0.3001.6503 21.54 (=νd2)  5* 2.365 0.711  6* −26.314 0.682 1.5348 55.66(=νd3)  7* −7.335 0.050  8* 6.662 0.525 1.5348 55.66 (=νd4)  9* 5.2960.458 10* 253.193 0.539 1.5348 55.66 (=νd5) 11* −111.646 0.483 12*−7.804 0.600 1.5443 55.86 (=νd6) 13* −3.067 0.100 14* −10.030 (=r13)1.378 1.6503 21.54 (=νd7) 15* −16.894 (=r14) 0.506 16* 23.658 0.6001.5348 55.66 (=νd8) 17*  2.901 (=r16) 0.340 18 Infinity 0.210 1.516864.20 19 Infinity 0.990 Image Plane Infinity Constituent Lens Data LensStart Surface Focal Length 1 1 6.69 2 4 −14.00 3 6 18.78 4 8 −55.78 5 10144.95 6 12 8.89 7 14 −41.22 8 16 −6.25 Composite Focal Length LensFocal Length 1, 2, 3 7.63 Aspheric Surface Data First Second FourthFifth Sixth Seventh Eighth Ninth Surface Surface Surface Surface SurfaceSurface Surface Surface k 0.000E+00 0.000E+00 0.000E+00 0.000E+000.000E+00 0.000E+00 0.000E+00 0.000E+00 A4 8.793E−04 2.599E−03−4.097E−02  −5.283E−02  7.952E−03 −1.583E−03  −2.056E−02  −1.496E−02  A6−1.165E−03  1.321E−04 1.088E−02 1.271E−02 −1.637E−03  3.089E−04−9.921E−04  −1.479E−03  A8 2.353E−04 −1.247E−04  −2.047E−03  −3.129E−03 6.994E−04 2.398E−05 1.162E−04 −6.081E−05  A10 −2.895E−05  3.136E−061.494E−04 4.074E−04 −8.636E−05  0.000E+00 0.000E+00 0.000E+00 A120.000E+00 0.000E+00 0.000E+00 −3.393E−05  0.000E+00 0.000E+00 0.000E+000.000E+00 A14 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+000.000E+00 0.000E+00 0.000E+00 A16 0.000E+00 0.000E+00 0.000E+000.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 Tenth Eleventh TwelfthThirteenth Fourteenth Fifteenth Sixteenth Seventeenth Surface SurfaceSurface Surface Surface Surface Surface Surface k 0.000E+00 0.000E+000.000E+00 −1.747E+00  0.000E+00 0.000E+00 0.000E+00 −6.553E+00  A4−1.407E−02  −1.929E−02  −1.121E−02  2.214E−03 5.277E−03 1.003E−02−3.113E−02  −2.250E−02  A6 2.758E−03 −3.824E−04  −6.418E−04  1.127E−034.946E−04 −4.494E−03  1.036E−03 2.651E−03 A8 −8.920E−04  1.511E−04−2.679E−05  −6.564E−04  −1.233E−03  9.010E−04 3.938E−04 −2.410E−04  A107.522E−05 0.000E+00 0.000E+00 6.646E−05 2.977E−04 −1.145E−04 −5.178E−05  1.448E−05 A12 0.000E+00 0.000E+00 0.000E+00 0.000E+00−3.550E−05  8.797E−06 2.672E−06 −4.749E−07  A14 0.000E+00 0.000E+000.000E+00 0.000E+00 1.580E−06 −3.790E−07  −5.858E−08  6.350E−09 A160.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 7.107E−09 3.590E−100.000E+00

The imaging lens in Example 2 satisfies all of conditional expressions(1) to (12) as shown in Table 8.

FIG. 4 shows spherical aberration (mm), astigmatism (mm), and distortion(%) of the imaging lens in Example 2. As shown in FIG. 4, eachaberration is corrected properly.

EXAMPLE 3

Basic lens data are shown in below Table 3.

TABLE 3 Table 3 Unit [mm] f = 8.04 Fno = 1.6 ω(°) = 32.0 Surface DataSurface Curvature Surface Refractive Abbe Number i Radius r Distance dIndex Nd Number νd (Object) Infinity Infinity  1* 4.103 1.230 1.544355.86 (=νd1)  2* −27.753 0.000  3(Stop) Infinity 0.030  4* 3.369 0.3091.6503 21.54 (=νd2)  5* 2.381 0.929  6* −11.320 0.646 1.5348 55.66(=νd3)  7* −5.835 0.050  8* 81.765 0.510 1.6503 21.54 (=νd4)  9* 30.7820.050 10* 4.661 0.449 1.5348 55.66 (=νd5) 11* 4.790 1.077 12* −5.8990.652 1.5443 55.86 (=νd6) 13* −2.951 0.100 14* −10.761 (=r13) 1.3331.6142 25.58 (=νd7) 15* −13.519 (=r14) 0.429 16* 121.143 0.600 1.534855.66 (=νd8) 17*  3.270 (=r16) 0.340 18 Infinity 0.210 1.5168 64.20 19Infinity 0.964 Image Plane Infinity Constituent Lens Data Lens StartSurface Focal Length 1 1 6.66 2 4 −14.23 3 6 21.63 4 8 −76.21 5 10146.22 6 12 10.06 7 14 −105.20 8 16 −6.29 Composite Focal Length LensFocal Length 1, 2, 3 7.94 Aspheric Surface data First Second FourthFifth Sixth Seventh Eighth Ninth Surface Surface Surface Surface SurfaceSurface Surface Surface k 0.000E+00 0.000E+00 0.000E+00 0.000E+000.000E+00 0.000E+00 0.000E+00 0.000E+00 A4 1.327E−03 2.083E−03−3.974E−02  −5.096E−02  1.086E−02 2.907E−03 −1.442E−02  −1.144E−02  A6−1.199E−03  7.487E−04 1.139E−02 1.304E−02 −2.093E−03  7.891E−042.008E−03 −7.330E−04  A8 2.627E−04 −2.155E−04  −2.023E−03  −3.178E−03 7.399E−04 −2.408E−04  −7.997E−04  1.653E−04 A10 −2.953E−05  7.596E−061.416E−04 4.242E−04 −1.091E−04  0.000E+00 9.894E−05 0.000E+00 A120.000E+00 0.000E+00 0.000E+00 −3.415E−05  0.000E+00 0.000E+00 0.000E+000.000E+00 A14 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+000.000E+00 0.000E+00 0.000E+00 A16 0.000E+00 0.000E+00 0.000E+000.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 Tenth Eleventh TwelfthThirteenth Fourteenth Fifteenth Sixteenth Seventeenth Surface SurfaceSurface Surface Surface Surface Surface Surface k 5.757E−01 4.969E−013.360E−01 −1.856E+00  0.000E+00 0.000E+00 0.000E+00 −7.683E+00  A4−1.515E−02  −1.257E−02  −3.038E−03  −2.535E−03  −5.949E−04  8.085E−03−2.818E−02  −2.148E−02  A6 −8.900E−04  −3.900E−04  6.876E−04 1.438E−031.497E−03 −4.226E−03  1.107E−03 2.688E−03 A8 1.139E−04 −5.921E−05 −2.187E−04  −5.375E−04  −1.256E−03  8.919E−04 3.887E−04 −2.418E−04  A100.000E+00 0.000E+00 0.000E+00 5.146E−05 2.933E−04 −1.147E−04 −5.223E−05  1.434E−05 A12 0.000E+00 0.000E+00 0.000E+00 0.000E+00−3.619E−05  8.832E−06 2.664E−06 −4.769E−07  A14 0.000E+00 0.000E+000.000E+00 0.000E+00 1.731E−06 −3.784E−07  −5.801E−08  6.549E−09 A160.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 6.966E−09 3.891E−100.000E+00

The imaging lens in Example 3 satisfies all of conditional expressions(1) to (12) as shown in Table 8.

FIG. 6 shows spherical aberration (mm), astigmatism (mm), and distortion(%) of the imaging lens in Example 3. As shown in FIG. 6, eachaberration is corrected properly.

EXAMPLE 4

Basic lens data are shown in below Table 4.

TABLE 4 Table 4 Unit [mm] f = 9.62 Fno = 1.4 ω(°) = 35.4 Surface DataSurface Curvature Surface Refractive Abbe Number i Radius r Distance dIndex Nd Number νd (Object) Infinity Infinity  1* 6.654 1.440 1.544355.86 (=νd1)  2* −52.527 0.007  3(Stop) Infinity 0.030  4* 28.912 0.8421.5348 55.66 (=νd2)  5* −118.994 0.025  6* 5.861 0.582 1.6503 21.54(=νd3)  7* 3.611 1.180  8* −56.607 1.153 1.5348 55.66 (=νd4)  9* −20.0900.030 10* 29.194 1.420 1.5348 55.66 (=νd5) 11* 20.931 0.717 12* −71.2711.060 1.5443 55.86 (=νd6) 13* −4.273 0.030 14* 39.334 (=r13) 1.3141.6142 25.58 (=νd7) 15* 12.785 (=r14) 1.091 16* −596.915 0.976 1.534855.66 (=νd8) 17*  4.724 (=r16) 0.600 18 Infinity 0.210 1.5168 64.20 19Infinity 0.707 Image Plane Infinity Constituent Lens Data Lens StartSurface Focal Length 1 1 10.94 2 4 43.58 3 6 −16.11 4 8 57.60 5 10−147.07 6 12 8.30 7 14 −31.43 8 16 −8.76 Composite Focal Length LensFocal Length 1, 2, 3 15.12 Aspheric Surface data First Second FourthFifth Sixth Seventh Eighth Ninth Surface Surface Surface Surface SurfaceSurface Surface Surface k 0.000E+00 0.000E+00 0.000E+00 0.000E+000.000E+00 0.000E+00 0.000E+00 0.000E+00 A4 −3.044E−04  3.227E−059.688E−04 1.467E−04 −1.060E−02  −1.329E−02  7.142E−04 −1.174E−03  A6−1.134E−04  5.863E−05 8.367E−06 −5.099E−06  1.133E−03 1.165E−03−4.235E−04  −2.137E−04  A8 7.029E−06 −4.682E−06  6.253E−06 −7.302E−06 −9.659E−05  −1.134E−04  2.352E−05 −7.893E−06  A10 −5.055E−07 −1.102E−07  −3.811E−07  2.230E−07 3.085E−06 4.749E−06 −1.274E−06 1.974E−06 A12 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00−1.938E−07  0.000E+00 0.000E+00 A14 0.000E+00 0.000E+00 0.000E+000.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 A16 0.000E+000.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00Tenth Eleventh Twelfth Thirteenth Fourteenth Fifteenth SixteenthSeventeenth Surface Surface Surface Surface Surface Surface SurfaceSurface k 0.000E+00 0.000E+00 0.000E+00 −2.212E+00  0.000E+00 0.000E+000.000E+00 −6.517E+00  A4 −5.103E−03  −5.227E−03  −2.272E−03  1.136E−032.994E−04 3.755E−04 −6.789E−03  −5.093E−03  A6 4.127E−06 −1.359E−04 2.129E−04 1.929E−04 −6.053E−05  −4.308E−04  1.284E−04 2.558E−04 A81.013E−05 2.546E−06 −3.919E−05  −2.471E−05  −4.085E−05  3.645E−051.574E−05 −9.904E−06  A10 0.000E+00 0.000E+00 1.324E−06 8.844E−075.056E−06 −1.847E−06  −8.775E−07  2.414E−07 A12 0.000E+00 0.000E+000.000E+00 0.000E+00 −2.651E−07  5.787E−08 1.751E−08 −3.223E−09  A140.000E+00 0.000E+00 0.000E+00 0.000E+00 5.185E−09 −1.028E−09 −1.262E−10  1.835E−11 A16 0.000E+00 0.000E+00 0.000E+00 0.000E+000.000E+00 7.869E−12 0.000E+00 0.000E+00

The imaging lens in Example 4 satisfies all of conditional expressions(1) to (12) as shown in Table 8.

FIG. 8 shows spherical aberration (mm), astigmatism (mm), and distortion(%) of the imaging lens in Example 4. As shown in FIG. 8, eachaberration is corrected properly.

EXAMPLE 5

Basic lens data are shown in below Table 5.

TABLE 5 Table 5 Unit [mm] f = 9.76 Fno = 1.4 ω(°) = 35.0 Surface DataSurface Curvature Surface Refractive Abbe Number i Radius r Distance dIndex Nd Number νd (Object) Infinity Infinity  1* 12.085 1.383 1.544355.86 (=νd1)  2* −22.067 0.046  3* 52.315 0.976 1.5348 55.66 (=νd2)  4*−45.642 0.083  5 (Stop) Infinity 0.168  6* 4.997 0.702 1.6503 21.54(=νd3)  7* 3.241 1.115  8* 33.871 1.819 1.5348 55.66 (=νd4)  9* −11.3260.197 10* 20.175 0.847 1.5348 55.66 (=νd5) 11* 11.042 0.966 12* −32.1051.387 1.5443 55.86 (=νd6) 13* −4.516 0.030 14* 28.241 (=r13)  1.6771.6142 25.58 (=νd7) 15* 9.216 (=r14) 1.050 16* 16.578 0.976 1.5348 55.66(=νd8) 17* 4.241 (=r16) 0.550 18 Infinity 0.210 1.5168 64.20 19 Infinity0.619 Image Plane Infinity Constituent Lens Data Lens Start SurfaceFocal Length 1 1 14.55 2 3 45.74 3 6 −16.84 4 8 16.10 5 10 −47.13 6 129.49 7 14 −23.04 8 16 −10.96 Composite Focal Length Lens Focal Length 1,2, 3 22.62 Aspheric Surface data First Second Third Fourth Sixth SeventhEighth Ninth Surface Surface Surface Surface Surface Surface SurfaceSurface k 0.000E+00 0.000E+00 0.000E+00 0.000E+00 −1.696E−01  −2.347E−010.000E+00 0.000E+00 A4 −4.135E−04  5.471E−04 1.066E−03 −1.202E−04 −1.085E−02  −1.476E−02 2.274E−04 −2.481E−03  A6 −5.549E−05  6.748E−053.489E−05 1.116E−04 1.028E−03  1.177E−03 −2.336E−04  −9.496E−05  A84.888E−06 −3.587E−06  3.711E−06 −5.746E−06  −8.211E−05  −1.192E−042.420E−05 1.870E−06 A10 −1.265E−07  2.830E−08 −3.416E−07  −2.968E−08 3.033E−06  5.844E−06 −2.312E−06  −3.985E−07  A12 0.000E+00 0.000E+000.000E+00 0.000E+00 −4.838E−08  −1.957E−07 0.000E+00 0.000E+00 A140.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00  0.000E+00 0.000E+000.000E+00 A16 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 Tenth Eleventh Twelfth ThirteenthFourteenth Fifteenth Sixteenth Seventeenth Surface Surface SurfaceSurface Surface Surface Surface Surface k 0.000E+00 0.000E+00 0.000E+00−1.537E+00  0.000E+00  0.000E+00 0.000E+00 −5.064E+00  A4 −6.384E−03 −4.574E−03  −8.538E−04  −3.218E−04  −2.096E−03  −1.428E−03 −1.018E−02 −6.167E−03  A6 −1.112E−04  −3.509E−05  2.978E−04 1.867E−04 4.652E−05−3.814E−04 2.357E−04 2.863E−04 A8 6.306E−06 −4.989E−06  −3.947E−05 −2.354E−05  −4.117E−05   3.678E−05 1.539E−05 −1.010E−05  A10 0.000E+000.000E+00 1.143E−06 9.332E−07 4.988E−06 −1.893E−06 −8.960E−07  2.530E−07A12 0.000E+00 0.000E+00 0.000E+00 0.000E+00 −2.694E−07   5.840E−081.713E−08 −3.572E−09  A14 0.000E+00 0.000E+00 0.000E+00 0.000E+005.378E−09 −9.962E−10 −1.163E−10  2.053E−11 A16 0.000E+00 0.000E+000.000E+00 0.000E+00 0.000E+00  7.125E−12 0.000E+00 0.000E+00

The imaging lens in Example 5 satisfies all of conditional expressions(1) to (12) as shown in Table 8.

FIG. 10 shows spherical aberration (mm), astigmatism (mm), anddistortion (%) of the imaging lens in Example 5. As shown in FIG. 10,each aberration is corrected properly.

EXAMPLE 6

Basic lens data are shown in below Table 6.

TABLE 6 Table 6 Unit [mm] f = 10.78 Fno = 1.4 ω(°) = 32.3 Surface DataSurface Curvature Surface Refractive Abbe Number i Radius r Distance dIndex Nd Number νd (Object) Infinity Infinity  1* 8.012 1.441 1.544355.86 (=νd1)  2* 500.000 0.182  3 (Stop) Infinity 0.025  4* 31.059 0.9471.5348 55.66 (=νd2)  5* 104.847 0.033  6* 6.665 0.621 1.6503 21.54(=νd3)  7* 4.265 0.879  8* 14.405 1.516 1.5348 55.66 (=νd4)  9* −158.0490.030 10* 8.339 0.784 1.5348 55.66 (=νd5) 11* 7.732 1.821 12* −113.6091.485 1.5443 55.86 (=νd6) 13* −6.401 0.030 14* 33.865 (=r13) 2.0551.6142 25.58 (=νd7) 15* 10.413 (=r14) 0.980 16* 9.443 1.067 1.5348 55.66(=νd8) 17*  4.104 (=r16) 0.600 18 Infinity 0.210 1.5168 64.20 19Infinity 0.608 Image Plane Infinity Constituent Lens Data Lens StartSurface Focal Length 1 1 14.94 2 4 82.15 3 6 −20.29 4 8 24.76 5 10−361.26 6 12 12.40 7 14 −25.33 8 16 −14.59 Composite Focal Length LensFocal Length 1, 2, 3 24.99 Aspheric Surface data First Second FourthFifth Sixth Seventh Eighth Ninth Surface Surface Surface Surface SurfaceSurface Surface Surface k 0.000E+00 0.000E+00 0.000E+00 0.000E+000.000E+00 0.000E+00 0.000E+00  0.000E+00 A4 −3.086E−04  −1.119E−04 1.145E−03 1.926E−04 −8.542E−03  −1.064E−02  6.364E−04 −1.035E−03 A6−5.894E−05  5.614E−05 −2.107E−05  −9.174E−06  8.311E−04 8.898E−04−2.378E−04  −1.291E−04 A8 3.949E−06 −3.523E−06  2.641E−06 −4.940E−06 −5.645E−05  −7.118E−05  1.354E−05 −8.130E−07 A10 −1.950E−07  5.667E−09−2.871E−07  1.138E−07 1.774E−06 3.103E−06 −4.160E−07   2.915E−07 A121.125E−09 0.000E+00 6.407E−09 2.517E−09 −1.678E−08  −7.492E−08 0.000E+00 −4.761E−09 A14 0.000E+00 0.000E+00 0.000E+00 0.000E+000.000E+00 0.000E+00 0.000E+00  0.000E+00 A16 0.000E+00 0.000E+000.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00  0.000E+00 TenthEleventh Twelfth Thirteenth Fourteenth Fifteenth Sixteenth SeventeenthSurface Surface Surface Surface Surface Surface Surface Surface k0.000E+00 0.000E+00 0.000E+00 −2.119E+00  0.000E+00 0.000E+00 0.000E+00−4.030E+00 A4 −5.713E−03  −4.106E−03  −5.672E−04  6.260E−08 −9.062E−04 −4.136E−04  −8.951E−03  −5.200E−03 A6 −2.956E−05  −5.567E−05  1.634E−048.574E−05 −2.403E−05  −2.974E−04  1.626E−04  2.214E−04 A8 −2.817E−06 1.167E−06 −2.484E−05  −1.597E−05  −2.330E−05  2.361E−05 1.011E−05−6.456E−06 A10 3.099E−07 0.000E+00 6.637E−07 5.766E−07 2.815E−06−1.026E−06  −4.948E−07   1.285E−07 A12 0.000E+00 0.000E+00 0.000E+000.000E+00 −1.283E−07  2.740E−08 8.047E−09 −1.403E−09 A14 0.000E+000.000E+00 0.000E+00 0.000E+00 2.058E−09 −4.235E−10  −4.607E−11  5.793E−12 A16 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+002.881E−12 0.000E+00  0.000E+00

The imaging lens in Example 6 satisfies all of conditional expressions(1) to (12) as shown in Table 8.

FIG. 12 shows spherical aberration (mm), astigmatism (mm), anddistortion (%) of the imaging lens in Example 6. As shown in FIG. 12,each aberration is corrected properly.

EXAMPLE 7

Basic lens data are shown in below Table 7.

TABLE 7 Table 7 Unit [mm] f = 10.11 Fno = 1.2 ω(°) = 34.0 Surface DataSurface Curvature Surface Refractive Abbe Number i Radius r Distance dIndex Nd Number νd (Object) Infinity Infinity  1* 10.402 1.500 1.544355.86 (=νd1)  2* −20.361 0.005  3 (Stop) Infinity 0.030  4* 55.788 1.0001.5348 55.66 (=νd2)  5* −580.859 0.028  6* 6.296 0.695 1.6503 21.54(=νd3)  7* 4.057 1.303  8* 50.551 1.425 1.5348 55.66 (=νd4)  9* −94.3250.217 10* 9.374 1.016 1.5348 55.66 (=νd5) 11* 9.164 1.085 12* 57.0361.611 1.5443 55.86 (=νd6) 13* −5.241 0.030 14* 17.166 (=r13)  1.5751.6503 21.54 (=νd7) 15* 7.582 (=r14) 1.191 16* 12.898 1.041 1.5348 55.66(=νd8) 17* 4.278 (=r16) 0.620 18 Infinity 0.210 1.5168 64.20 19 Infinity0.608 Image Plane Infinity Constituent Lens Data Lens Start SurfaceFocal Length 1 1 12.87 2 4 95.22 3 6 −19.98 4 8 61.75 5 10 1114.45 6 128.90 7 14 −22.32 8 16 −12.49 Composite Focal Length Lens Focal Length 1,2, 3 20.37 Aspheric Surface data First Second Fourth Fifth Sixth SeventhEighth Ninth Surface Surface Surface Surface Surface Surface SurfaceSurface k −2.764E−01  −9.059E+00  5.206E+01 0.000E+00 0.000E+00 0.000E+00 0.000E+00  0.000E+00 A4 −4.787E−04  4.425E−05 1.101E−03−1.120E−04  −8.629E−03  −1.105E−02 5.150E−04 −1.316E−03 A6 −6.870E−05 5.482E−05 −2.443E−05  −3.613E−06  7.967E−04  8.693E−04 −2.429E−04 −1.685E−04 A8 5.218E−06 −3.296E−06  3.312E−06 −4.778E−06  −5.730E−05 −7.483E−05 1.449E−05 −1.080E−06 A10 −1.856E−07  3.192E−08 −3.036E−07 1.336E−07 1.704E−06  3.067E−06 −7.901E−07   3.381E−07 A12 1.110E−09−1.753E−11  5.050E−09 −3.009E−10  −9.932E−09  −7.107E−08 −2.307E−09 −1.198E−08 A14 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00−1.132E−10 0.000E+00  0.000E+00 A16 0.000E+00 0.000E+00 0.000E+000.000E+00 0.000E+00  0.000E+00 0.000E+00  0.000E+00 Tenth EleventhTwelfth Thirteenth Fourteenth Fifteenth Sixteenth Seventeenth SurfaceSurface Surface Surface Surface Surface Surface Surface k 0.000E+000.000E+00 0.000E+00 −2.951E+00  0.000E+00  0.000E+00 0.000E+00−4.467E+00 A4 −5.112E−03  −4.196E−03  −7.192E−04  −4.503E−05 −1.324E−03  −1.769E−03 −8.461E−03  −5.138E−03 A6 −2.888E−05  −4.279E−05 1.680E−04 8.623E−05 −3.618E−05  −2.721E−04 1.614E−04  2.141E−04 A8−3.473E−06  −6.380E−07  −2.502E−05  −1.371E−05  −2.444E−05   2.353E−059.954E−06 −6.403E−06 A10 2.746E−07 0.000E+00 6.781E−07 3.956E−072.934E−08 −1.042E−06 −4.939E−07   1.343E−07 A12 0.000E+00 0.000E+000.000E+00 4.650E−09 −1.303E−07   2.771E−08 8.192E−09 −1.604E−09 A140.000E+00 0.000E+00 0.000E+00 0.000E+00 2.047E−09 −4.203E−10 −4.839E−11  7.750E−12 A16 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 2.781E−12 0.000E+00  0.000E+00

The imaging lens in Example 7 satisfies all of conditional expressions(1) to (12) as shown in Table 8.

FIG. 14 shows spherical aberration (mm), astigmatism (mm), anddistortion (%) of the imaging lens in Example 7. As shown in FIG. 14,each aberration is corrected properly.

Below Table 8 shows each parameter, and conditional expressions (1) to(12) relating to Examples 1 to 7.

TABLE 8 Example1 Example2 Example3 Example4 Example5 Example6 Example7Parameters f 11.68 7.75 8.04 9.62 9.76 10.78 10.11 Σ d 15.35 8.11 8.3911.90 13.42 13.90 13.75 Ph82 4.33 1.92 1.92 3.27 3.12 3.77 3.58 r1310.383 −10.030 −10.761 39.334 28.241 33.865 17.166 r14 5.263 −16.894−13.519 12.785 9.216 10.413 7.582 r16 4.227 2.901 3.270 4.724 4.2414.104 4.278 f7 −17.38 −41.22 −105.20 −31.43 −23.04 −25.33 −22.32 f8−86.89 −6.25 −6.29 −8.76 −10.96 −14.59 −12.49 νd8 55.66 55.66 55.6655.66 55.66 55.66 55.66 νd7 21.54 21.54 25.58 25.58 25.58 25.58 21.54f123 16.74 7.63 7.94 15.12 22.62 24.99 20.37 TTL 17.04 9.58 9.84 13.3414.73 15.24 15.11 ih 7.99 5.06 5.06 7.00 7.00 7.00 7.00 Fno 1.4 1.6 1.61.4 1.4 1.4 1.2 f4 −1702.49 −55.78 −76.21 57.60 16.10 24.76 61.75 f514.52 144.95 146.22 −147.07 −47.13 −361.26 1114.45 f6 −67.86 8.89 10.068.30 9.49 12.40 8.90 Conditional Expressions (1)0.5 < Σ d/f < 2.1 1.311.05 1.04 1.24 1.38 1.29 1.36 (2)0.1 < Ph82/ih < 0.9 0.54 0.38 0.38 0.470.45 0.54 0.51 (3)0.3 < r13/r14 < 4.9 1.97 0.59 0.80 3.08 3.06 3.25 2.26(4)0.2 < r16/f < 0.8 0.36 0.37 0.41 0.49 0.43 0.38 0.42 (5)0.4 <|f/f7| + |f/f8| < 2.2 0.81 1.43 1.35 1.40 1.31 1.16 1.26 (6)15 < νd8 −νd7 < 52 34.13 34.13 30.09 30.09 30.09 30.09 34.13 (7)f123/f < 3.5 1.430.98 0.99 1.57 2.32 2.32 2.02 (8)−1.9 < f/f8 < −0.07 −0.13 −1.24 −1.28−1.10 −0.89 −0.74 −0.81 (9)0.6 < TTL/2ih < 1.3 1.07 0.95 0.97 0.95 1.051.09 1.08 (10)0.5 < ih/f < 0.9 0.68 0.65 0.63 0.73 0.72 0.65 0.69(11)Fno ≦ 1.8 1.40 1.60 1.60 1.40 1.40 1.40 1.20 (12)|f/f4| + |f/f5| +|f/f6| < 2.8 0.98 1.07 0.96 1.39 1.84 1.33 1.31

As explained so far, if the imaging lens according to the presentinvention of eight constituent is applied to an increasingly compact andlow-profile smartphone, or mobile terminals, or a game console, or aninformation terminal such as a PC and a robot, or a home appliance or acar with a camera function, it can contribute to the low-profileness andlow f value of the camera, and realize high-performance of camera.

An effect of the present invention is to satisfy demand oflow-profileness and low F value, and obtain a compact imaging lenshaving high resolution with correction of aberrations.

1. An imaging lens forming an image of an object a solid-state imagesensor, in which the lenses are arranged in order from an object side toan image side, comprising: a first lens having positive refractive powerand a convex surface on an object side near an optical axis, a secondlens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventhlens and a eighth lens having a concave surface on an image side nearthe optical axis as double-sided aspheric lens, wherein the second toseventh lenses each have at least one aspheric surface, and the eighthlens has pole points off an optical axis on the aspheric image-sidesurface.
 2. An imaging lens according to claim 1, wherein a conditionalexpression (1) below is satisfied:0.5<Σd/f<2.1   (1) where f denotes the focal length of the overalloptical system, and Σd denotes a distance on an optical axis from theobject-side surface of a first lens to the image-side surface of theeighth lens.
 3. An imaging lens according to claim 1, wherein the firstlens to the eighth lens are arranged with an air interval withoutjoining lens surface of lenses adjacent each other.
 4. An imaging lensaccording to claim 1, wherein a conditional expression (2) below issatisfied:0.1<Ph82/ih<0.9   (2) where Ph82 denotes a height perpendicular to theoptical axis of the pole point formed on an image-side surface of theeighth lens; ih denotes maximum image height.
 5. An imaging lensaccording to claim 1, wherein the second lens has a convex surface onthe object side near the optical axis.
 6. An imaging lens according toclaim 1, wherein the third lens is meniscus near the optical axis.
 7. Animaging lens according to claim 1, wherein the seventh lens has negativerefractive power.
 8. An imaging lens according to claim 7, wherein theseventh lens is meniscus near the optical axis.
 9. An imaging lensaccording to claim 8, wherein a conditional expression (3) below issatisfied:0.3<|r13/r14|<4.9   (3) where r13 denotes the curvature radius near anoptical axis of the object-side surface of the seventh lens, and r14denotes the curvature radius near the optical axis of the image-sidesurface of the seventh lens.
 10. An imaging lens according to claim 1,wherein the eighth lens has negative refractive power and consists ofplastic material.
 11. An imaging lens according to claim 10, wherein aconditional expression (4) below is satisfied:0.2<r16/f<0.8   (4) Where f denotes a focal length of the overalloptical system, and r16 denotes the curvature radius of the image-sidesurface of the eighth lens.
 12. An imaging lens according to claim 1,wherein a conditional expression (5) below is satisfied:0.4<|f/f7|+|f/f8|<2.2   (5) where f denotes a focal length of theoverall optical system, f7 denotes a focal length of the seventh lens,and f8 denotes a focal length of the eighth lens.
 13. An imaging lensaccording to claim 1, wherein a conditional expression (6) below issatisfied:15<νd8−νd7<52   (6) where νd7 denotes an Abbe number of the seventh lensat d-ray, and νd8 is an Abbe number of the eighth lens at d-ray.
 14. Animaging lens according to claim 1, wherein a conditional expression (7)below is satisfied:f123/f<3.5   (7) where f denotes a focal length of the overall opticalsystem, f123 denotes a composite focal length of the first, second andthird lenses.
 15. An imaging lens according to claim 10, wherein aconditional expression (8) below is satisfied:−1.9<f/f8<−0.07   (8) where f denotes a focal length of the overalloptical system, f8 denotes a focal length of the eighth lens.
 16. Animaging lens according to claim 1, wherein a conditional expression (9)below is satisfied:0.6<TTL/2ih<1.3   (9) where TTL denotes a total track length, ih denotesmaximum image height.
 17. An imaging lens according to claim 1, whereina conditional expression (10) below is satisfied:0.5<ih/f<0.9   (10) where f denotes a focal length of the overalloptical system, ih denotes maximum image height.
 18. An imaging lensaccording to claim 1, wherein a conditional expression (11) below issatisfied:Fno≦1.8   (11) where Fno denotes F-number.
 19. An imaging lens accordingto claim 1, wherein a conditional expression (12) below is satisfied:|f/f4|+|f/f5|+|f/f6|<2.8   (12) where f denotes a focal length of theoverall optical system, f4 denotes a focal length of the fourth lens, f5denotes a focal length of the fifth lens, f6 denotes a focal length ofthe sixth lens.
 20. An imaging lens according to claim 3, wherein aconditional expression (2) below is satisfied:0.1<Ph82/ih<0.9   (2) where Ph82 denotes a height perpendicular to theoptical axis of the pole point formed on an image-side surface of theeighth lens; ih denotes maximum image height.